Skin and Integument Histology Flashcards
The integument is an organ consisting of
epithelium, connective tissue, glands and sensory receptors
What are the functions of integument?
barrier and protection against physical, chemical & biological agent– maintains homeostasis by regulating temperature and water loss– Tactile, pain, & temperature sensation
What are the two types of skin?
thick and thin
Do thick and thin skin both have epidermis and dermis?
Yes
What type of epithelium is the epidermis?
keratinized stratified squamous epithelium
What type of tissue is the dermis classified as?
CT
Is the hypodermic part of the skin?
No. The hypodermis cushions and insulates the body.
What does the epidermis-dermis junction consist of?
dermal papillae and interpapillary pegsepidermal protrusions - named interpapillary pegs - into the dermis create dermal papillae
The attachment of the epidermis to the basal lamina is made by what?
hemidesmosomes
The apical border of the epidermis forms what structure?
primary epidermal! ridges
What protrudes in the middle of a primary dermal ridge?
an interpapillary peg of the epidermis
What is the primary role of Dermal papillae – inter papillary pegs?
strengthen grip of epidermis to dermis
What can make the primary epidermal ridges deeper?
mechanical stress
What part of the skin is the source of fingerprint?
Primary epidermis ridgesThey are genetically unique – no two people have the same fingerprint (dermatoglyphic – science of fingerprints)
Where are keratinocytes made?
basal layer of skin
What happens when keratinocytes migrate to the skin surface?
They are filled with keratin, die, and eventually slough off
What layer of the epidermis is closest to the dermis?
stratum basale
What kinds of cells are present in the stratum basale?
cuboidal to low columnar cells
Cells in the stratum basale are connected how?
interconnected by desmosomaljunctions.
Are cells in the stratum basale connected to the dermis?
Yes. has hemidesmosomal junctions with basal lamina.
Where does synthesis of lamellar bodies begin?
stratum basale
How many cell layers is the stratum basale?
single layer of mitotically active cells.
Directly on top of the stratum basale is what cell layer? How many cell layers is it?
stratum spinosum, the prickle cell layerseveral cells thick
Adjacent cells of the stratum basale are connected by?
desmosomes (spines)
Cells in upper part s. spinosum begin to make what?
karatohyalin granules (which contribute to keratinization)
What cell layer lays directly above the s. spinosum?
the Stratum granulosum (aka the mature synthetic layer)
How many cell layers is the stratum granlosum?
1-3 layers
What do keratohyalin granules contain?
cystine and histidine-rich amino acids & precursors for filaggrin and trichohyalin
Appearance of granules is a clinical marker for final stage of what to occur?
apoptosis
What does Filaggrin do?
aggregates tonofibrils - turning granular cells into cornified cells – a process called keratinization
What is the role of Trichohyalin?
modulates the migration of keratinized cells into the s. corneum (takes 2-6 hrs)
What cell layer is directly superficial to the stratum granlosum?
stratum corneum (the surface layer of the skin)
What is Desquamation regulated by?
proteolytic degradation (serine pepidases) of cells’ desmosomes
What are the major epidermis differences in thin vs. thick skin?
Thin skin has: • no surface ridges• stratum corneum is thinner– typically no s. lucidum sublayer • granule layer absent or poorlydefined• presence of pigment in thin skin
T or F. Thin skin has fewer dermal papillae & height of DP is reduced in thin skin
T
Does thick skin have hair?
No. Thin skin has hairs and sebaceous glands, thick skin doesn’t
What are the two components of the water barrier of the skin?
lipid envelopecell envelope
What is the lipid envelope formed by?
produced by exocytosis of lamellar bodies from s. granulosum cellslipids use ester bonds to attach to outer surface of cells in s. corneum
What is the cell envelope formed by?
made by cross- linking of insoluble proteins situated on the intracellular membrane of s. corneum cells (more superficial than the lipid envelope)
What proteins are responsible for making the cell envelope?
small proline-rich and larger LORICRIN proteins
What is the major cell type in the epidermis?What is it’s role?Do they regenerate?
Keratinocytesprovide protection against and enable physical wear and tear and supports water barrierYes
What do melanocytes do in the epidermis?
provide UV protection and skin pigmentation
What do Langerhan’s cells do in the epidermis?
provide immunologic protection
What do Merkel cells do in the epidermis?
provide sensory reception
Where are melanocytes found in the epidermis? What do they produce?
s. basale (migrate from neural crest)melaninNOTE: melanocytes have dendritic processes that extends from s. basal layer into stratum spinosum
Where is melanin found in the s. basale layer?
found in membrane limited bodies called melanosomes
Where do melanosomes come from?
come from Golgi as premelanosomnes (Premelanosomes do not become melanized until they reach the dendrites)
How is melanin made?
made by oxidation of tyrosine to 3,4- dihydroxyphenylalanine (DOPA) by tyrosinase, then DOPA into melanin
What stimulates melanin synthesis and secretion?
MSH
What are the two kinds of melanin?
eumelanin (black) and pheomelanin(yellow red)
How does abundant pigmentation occur?
• basal keratinocytes phagocytize the dendrite tips of melanocytes• The melanosomes take up positions on the “sunny side” of the nucleus and thus protect it from UV radiation
Are melanocytes pigmented in H and E staining? Why?
No. • melanocytes do not have desmosomal connections with adj basal keratinocytes - so they shrink away from adjacent cells during prep• Because of shrinkage and the absence of melanin in the cell body, they are identified as clear cells
Do dark and light skinned people have the same number of melanocytes?
Yes
What accounts for skin color difference?
• In dark skin:– more melanin is produced and transferred to keratinocytes– the melanosomes are larger and there are more of them – the melanosomes are more stable (degradation by lysosomes is slower)NOTE: In dark skin melanin may be seen in the upper part of the spinous layer in addition to the basal layer. Comparatively, in light skin the melanin in the basal layer may be so sparse as to be not immediately obvious.”
What happens during tanning?
At first there is a rapid darkening of existing pigment. Then, within a few days there is an increase in tyrosinase activity in melanocytes – producing more melanin
What is a basal cell carcinoma?
basal cells proliferation and invade dermisand hypodermisleast malignant but most common skin cancer (slow growing and rarely metastasize)easily cured by excision
What is a squamous cell carcinoma?
- arisesfromstratumspinosum- a scaly reddened elevation- most common on scalp, ears, dorsum of hands, and lower lip- grows rapidly, metastasizes early- can be cured by excision and/ or radiation if caught early
What layer of the epidermis are langerhan’s cells found?
s. spinosum (has dendrites!)
What is the role of langerhan’s cells?
are antigens-presenting cells as part of immune system”– migrate from epidermis to nearby lymph nodes where they present antigen to T lymphocytes”
What are langerhan cells derived from?
derived from stem cells in bone marrow
What are Merkel cells and what layer of the epidermis are they found?
modified epidermal cells in thes. basale layerinvolved in sensory reception and stain clear
The base of Merkel cells have what?
an expanded nerve terminal ending
A nerve fiber + a Merkel cell is called?
a Merkel’s corpuscle (tactile sensory receptors)
Which two layers of the epidermis originate there?
kartinocytes and Merkel’sLangerhan’s and melanocytes migrate
What are the two layers of the dermis?
• Papillary layer is loose connective tissue• Reticular layer is dense irregular CT
What is the hypodermic composed of?
large amount of adipose tissue
What kinds of fibers does the papillary layer of the dermis contain?
thin collagen (1 and III) and small elastic fibers.– also contains capillaries & small blood vessels– nerves and sensory receptorsNOTE: Reticular layer also contains courser collagen and elastic fibers and blood vessels, but they are larger
What are the two types of nerve endings in the integument?
free and encapsulated (enclosed in aconnective tissue capsule)
Where do free nerve endings terminate?
s. granulosum
What are the four types of encapsulated nerve endings?
Pacinian corpuscle, Meissner corpuscle, Ruffini’s corpuscle, & Krause’s end bulb.
Where are Meissner’s corpuscles found?
dermal papillae (of thick skin) on fingers and toes1 to 2 unmyelinated nerve fiber takes a circuitous route through stacks of flattened Schwann cells
Describe Pacinian corpuscles
Encapsulated receptor in deep dermis or hypodermis, abundant in fingertips• Fluid filled, concentric outer layers(core) of fibroblasts and collagen fibers• Concentric inner layers of Schwann cells• A single nerve fiber penetrates to center
What are some types of skin appendages?
• Hair follicles and hair• Finger nails• Sebaceous glands• Sweat glands– eccrine sweat glands – apocrine sweat glands
What are the three segments of a hair follicle?
• Infundibulum• Isthmus• Inferior segment
How do fair follicles develop?
Develop from invaginations of the epidermis into the dermis and hypodermis.
Describe the formation of hair follicles.
• Beneath the surface of the skin, epidermis turns into external root sheath.• The follicle expands at its base to form the bulb.– Bulb is invaginated by dermal papilla.– Cells surrounding the dermal papilla are called matrix cells, the germinative region of bulb.The matrix cells then differentiate into the internal root stealth and hair• Keratinization of the IRS and hair occurs in the keratogenous zone.– IRS cells have trichohyalin, contribute to keratinization.• The IRS does not emerge from the follicle. It is broken down at sebaceous gland canal• Hair has a cortex and medulla.• Surrounding the follicle is the dermal sheath, a dense irregular connective tissue.
Notes on Follicular budge of external root sheath
- Provides stem cells for hair growth and internal root sheath and sebaceous glands2. Stem cells reprogram when the epidermis is injured or lost in extensive skin burns and superficial skin wounds and participate in the initial resurfacing of the wound3. Thearrectorpilimuscleis attached to follicular bulge
Where are sebaceous glands found?
• Usually associated with hair follicles via pilosebaceous canal (but somethimes just discharge onto surface of epidermis)• are outgrowths from external root sheath of hair follicle
What do sebaceous glands release?
A fatty material – sebum - composed of disintegrated cells (the entire cell is the secretion- aka a holocrine secretion)Sebum coats hair and skin– vapor barrier, reduces water loss – protects skins from bacterial infections
How does sebum typically reach hair follicles?
through the pilosebaceous canal
T or F. Sebum production increases at puberty, decrease in older adults
T. It is involved in acne production
Nails rest on what?
rests on nail bed, continuous with s. basale and spinosum of epidermis. Note, no s. granulosum in epithelia of nail bed
What are the parts of a nail?
– Root: proximal part of nail overlapped by skin– Matrix: the germinative zone, contains the 4 cell types found in epidermis– Lunula: partially keratinized cells in underlying matrix
What causes the hardness of nails?
high sulfur content
Where are eccrine sweat glands found?
distributed over the entire body surface except for the lips and part of the external genitalia.
Where are apocrine sweat glands found?
limited to the axilla, areola and nipple of the mammary gland, and around the anus and the external genitalia.
What are the contents of eccrine sweat gland secretions?
watery hypotonic sweat with mostly water, NaCl, and a small amount of protein, urea, and ammoniaNaCl is reabsorbed in the duct to reduce salt loss
What are the two segments of eccrine sweat glands?
a secretory segment & a duct
What kind of epithelium does an eccrine sweat gland duct have?
stratified cuboidal epitheliumso does apocrine duct
What are the three cell types in the secretory segment of an eccrine sweat gland?
– Clear cells produce the watery component– Dark cells produce glycoprotein– Myoepithelial cells are involved in excretion
Eccrine SGs are stimulated by what kind of transmitter?
cholinergic transmitters
Apocrine SGs are innervated by what kind of transmitter?
adrenergic
When do apocrine sweat glands become functional?
puberty
What are the contents of apocrine sweat gland secretions?
viscous fluid with protein, carbohydrate, ammonia, lipid, and organic compounds– May contain pheromonessecretion odorless but gains odor when mixed with bacteria on skin surface
Comparison of eccrine and apocrine sweat glands
• Secretory segment of apocrine SG is wider than eccrine SG segment• Eccrine SGs responds to heat (and stress), apocrine to emotional and sensory stimuli• Eccrine SGs are functional at birth, apocrine at puberty• Eccrine distribution over much of body, apocrine restricted.”• Eccrine SG duct exits onto skin surface, apocrine SG duct exits into hair follicle. • Eccrine SGs are stimulated by cholinergic transmitters, which are usually associated w parasympathetic NS, but in this case the sympathetic NS • Apocrine SGs are stimulated adrenergic transmitters of the sympathetic NS
A first degree burn is limited to what level of the skin?
epidermis
A second degree burn is limited to what level of the skin?
damage tissue in the epidermis and upper region of the dermis
A third degree burn is limited to what level of the skin?
injury extends down to the hypodermis usually require skin graftsNOTE: Healing only occurs after first and second degree burns
What are some consequences of severe burns?
loss of body fluids (including proteins and electrolytes)leads to renal shutdown and circulatory shockmust replace lost fluids immediatelypatient must be fed intravenously to provide the immense caloric need to fuel tissue repairInfection - burned skin is sterile for around 24 hrs, then pathogens invade (and the immune system is depressed)must cover the burned area with a graft (pig skin, cadaver skin, engineered skin etc.)
What provide foci for regeneration of epidermis?
Hair follicles and sweat glands
